For troubleshooting monitor issues I plug in my computer to an external monitor (through HDMI or VGA, where applicable). If the monitor works and the display gets through then it's something wrong w/ your computer's hardware.
If plugging your computer to a TV works -- you should try downloading the newest BIOS version for your computer. Can't hurt.
Just my two cents,
I have purchased a desktop computer and I've used it for only a year then my system crashed. The last time I've boot my system it powerded on but did not make any boot sound except the cpu fan, the hard drives also run and the optical mouse did also have power but the keyboard did not show any light even when I pressed the num lock key and the scroll lock keys.
My desktops specification: intel core duo, 2Gig ddr2 RAM, 256mb ddr HIS radeon excallibur 9550 display driver, windows xp home edition, and two hardrives 80 gig and the other is 20 gig.
I've already tried installing my my video card to a friends desktop and it worked accordingly and as with the 2 gig ddr2 RAM is brand new and been tested by the store provider.
Is it the mother board or something else?